This document discusses image thresholding techniques for image segmentation. It describes thresholding as the basic first step for segmentation that partitions an image into foreground and background pixels based on intensity value. Simple thresholding uses a single cutoff value but can fail for complex histograms. Adaptive thresholding divides an image into sub-images and thresholds each individually to handle varying intensities better than simple thresholding. The document provides examples and algorithms to illustrate thresholding and its limitations and adaptations.